■Faculty | Faculty Division of Natural Sciences Research Group of Physics | |||

■Position | Assistant Professor |

Last Updated :2022/10/06

#### Contact Point

hohkicc.nara-wu.ac.jp#### Name (Japanese)

Hiroshi#### Name (Kana)

Oki

- Particle Physics Phenomenology
- Non-perturbative dynamics
- String theory
- Lattice Field Theory
- Theoretical Particle Physics

- Mar. 2017, 9999, Nara Women's University Faculty, Division of Natural Sciences
- Jul. 2015, Feb. 2017, RIKEN, RIKEN-BNL Research Center, Special Postdoctoral Researcher
- Apr. 2015, Jun. 2015, RIKEN, Quantum Hadron Physics Laboratory, Special Postdoctoral Researcher, Japan
- Sep. 2010, Mar. 2015, Nagoya University, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Research Assistant Professor, Japan
- Apr. 2009, Sep. 2010, Research Fellow of the Japan Society for the Promotion of Science, Japan

- Apr. 2005, Mar. 2010, Kyoto University, Faculty of Science, Japan
- Apr. 2001, Mar. 2005, Kanazawa University, Faculty of Science, Japan

- Special Seminar in Physics and Mathematics D, Nara Women's University, 99 Oct. 2019
- Special Seminar in Physics and Mathematics C, Nara Women's University, 99 Apr. 2019
- Particle Physics Seminar B, Nara Women's University, 99 Oct. 2018
- Special Seminar in Physics and Mathematics B, Nara Women's University, 99 Oct. 2018
- Exercises in Applied Complex Analysis, Nara Women's University, 99 Oct. 2018
- Particle Physics Seminar A, Nara Women's University, 99 Apr. 2018
- Special Seminar in Physics and Mathematics A, Nara Women's University, 99 Apr. 2018
- Quantum Field Theory II, Nara Women's University, 99 Oct. 2017
- Exercises in Quantum Mechanics I, Nara Women's University, 99 Oct. 2017
- Basic Quantum Mechanics, Nara Women's University, 99 Apr. 2017
- Introduction to Cosmology, Nara Women's University, 99 2017
- SCORE2019, Nara Women's University
- SCORE2017, Nara Women's University
- Special Seminar in Physics and Mathematics B, Nara Women's University, 99 Apr. 2020, Postgraduate courses
- Special Seminar in Physics and Mathematics D, Nara Women's University, 99 Apr. 2020, Postgraduate courses
- Quantum Field Theory B, Nara Women's University, 99 2018, Postgraduate courses

- Refereed, 12 Jul. 2021, 7, 068, 44
- Refereed, Physical Review D, American Physical Society (APS), Towards fully nonperturbative computations of inelastic ℓN scattering cross sections from lattice QCD, Hidenori Fukaya; Shoji Hashimoto; Takashi Kaneko; Hiroshi Ohki, 22 Dec. 2020, 102, 11, Scientific journal
- Refereed, Physical Review D, Modular flavor symmetry on a magnetized torus, Hiroshi Ohki; Shohei Uemura; Risa Watanabe, © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3. We study the modular invariance in magnetized torus models. The modular invariant flavor model is a recently proposed hypothesis for solving the flavor puzzle, where the flavor symmetry originates from modular invariance. In this framework, coupling constants such as Yukawa couplings are also transformed under the flavor symmetry. We show that the low-energy effective theory of magnetized torus models is invariant under a specific subgroup of the modular group. Since Yukawa couplings as well as chiral zero modes transform under the modular group, the above modular subgroup (referred to as modular flavor symmetry) provides a new type of modular invariant flavor models with D4×Z2, (Z4×Z2)⋊Z2, and (Z8×Z2)⋊Z2. We also find that conventional discrete flavor symmetries which arise in magnetized torus model are noncommutative with the modular flavor symmetry. Combining both symmetries, we obtain a larger flavor symmetry, which is the semidirect product of the conventional flavor symmetry and the modular flavor symmetry for the nonvanishing Wilson line. For the vanishing Wilson line, we have additional Z2 symmetry, i.e., parity, which is the unique common element between the conventional flavor symmetry and the modular flavor symmetry., Oct. 2020, 102, 8, Scientific journal
- Refereed, Journal of High Energy Physics, Gravitational waves from walking technicolor, Kohtaroh Miura; Hiroshi Ohki; Saeko Otani; Koichi Yamawaki, © 2019, The Author(s). We study gravitational waves from the first-order electroweak phase transition in the SU(Nc) gauge theory with Nf/Nc ≫ 1 (“large Nf QCD”) as a candidate for the walking technicolor, which is modeled by the U(Nf) × U(Nf) linear sigma model with classical scale symmetry (without mass term), particularly for Nf = 8 (“one-family model”). This model exhibits spontaneous breaking of the scale symmetry as well as the U(Nf) × U(Nf) radiatively through the Coleman-Weinberg mechanism à la Gildener-Weinberg, thus giving rise to a light pseudo dilaton (technidilaton) to be identified with the 125 GeV Higgs. This model possess a strong first-order electroweak phase transition due to the resultant Coleman-Weinberg type potential. We estimate the bubble nucleation that exhibits an ultra supercooling and then the signal for a stochastic gravitational wave produced via the strong first-order electroweak phase transition. We show that the amplitude can be reached to the expected sensitivities of the LISA., 01 Oct. 2019, 2019, 10, Scientific journal
- Refereed, Physical Review Letters, Novel |Vus | Determination Using Inclusive Strange τ Decay and Lattice Hadronic Vacuum Polarization Functions, Peter Boyle; Renwick James Hudspith; Taku Izubuchi; Andreas Jüttner; Christoph Lehner; Randy Lewis; Kim Maltman; Hiroshi Ohki; Antonin Portelli; Matthew Spraggs, © 2018 authors. Published by the American Physical Society. We propose and apply a new approach to determining |Vus| using dispersion relations with weight functions having poles at Euclidean (spacelike) momentum which relate strange hadronic τ decay distributions to hadronic vacuum polarization (HVP) functions obtained from lattice quantum chromodynamics. We show examples where spectral integral contributions from the region where experimental data have large errors or do not exist are strongly suppressed but accurate determinations of the relevant lattice HVP combinations remain possible. The resulting |Vus| agrees well with determinations from K physics and three-family Cabibbo-Kobayashi-Maskawa unitarity. Advantages of this new approach over the conventional hadronic τ decay determination employing flavor-breaking sum rules are also discussed., 16 Nov. 2018, 121, 20, Scientific journal
- Refereed, Physical Review D, Nucleon charges with dynamical overlap fermions, N. Yamanaka; S. Hashimoto; T. Kaneko; H. Ohki, © 2018 authors. Published by the American Physical Society. We calculate the scalar and tensor charges of the nucleon in 2+1-flavor lattice QCD, for which the systematics of the renormalization of the disconnected diagram is well controlled. Numerical simulations are performed at a single lattice spacing a=0.11 fm. We simulate four pion masses, which cover a range of mπ∼290-540 MeV, and a single strange quark mass close to its physical value. The statistical accuracy is improved by employing the so-called low-mode averaging technique and the truncated solver method. We study up, down, and strange quark contributions to the nucleon charges by calculating disconnected diagrams using the all-to-all quark propagator. Chiral symmetry is exactly preserved by using the overlap quark action to avoid operator mixing among different flavors, which complicates the renormalization of scalar and tensor matrix elements and leads to possibly large contamination to the small strange quark contributions. We also study the nucleon axial charge with a contribution from the disconnected diagram. Our results are in reasonable agreement with experiments and previous lattice studies., 25 Sep. 2018, 98, 5, Scientific journal
- Refereed, EPJ Web of Conferences, EDP Sciences, | Vus | determination from inclusive strange tau decay and lattice HVP, Peter Boyle; Renwick James Hudspith; Taku Izubuchi; Andreas Jüttner; Christoph Lehner; Randy Lewis; Kim Maltman; Hiroshi Ohki; Antonin Portelli; Matthew Spraggs, We propose and apply a novel approach to determining |Vus| which uses inclusive strange hadronic tau decay data and hadronic vacuum polarization functions (HVPs) computed on the lattice. The experimental and lattice data are related through dispersion relations which employ a class of weight functions having poles at space-like momentum. Implementing this approach using lattice data generated by the RBC/UKQCD collaboration, we show examples of weight functions which strongly suppress spectral integral contributions from the region where experimental data either have large uncertainties or do not exist while at the same time allowing accurate determinations of relevant lattice HVPs. Our result for |Vus| is in good agreement with determinations from K physics and 3-family CKM unitarity. The advantages of the new approach over the conventional sum rule analysis will be discussed., 26 Mar. 2018, 175, International conference proceedings
- Refereed, EPJ, Computing nucleon EDM on a lattice, M.~Abramczyk; S.~Aoki; T.~Blum; T.~Izubuchi; H.~Ohki; S.~Syritsyn, Jan. 2018, 175, 06027, International conference proceedings
- Refereed, On Lattice Calculation of Electric Dipole Moments and Form Factors of the Nucleon, M. Abramczyk; S. Aoki; T. Blum; T. Izubuchi; H. Ohki; S. Syritsyn, We analyze commonly used expressions for computing the nucleon electric dipole form factors (EDFF) $F_3$ and moments (EDM) on a lattice and find that they lead to spurious contributions from the Pauli form factor $F_2$ due to inadequate definition of these form factors when parity mixing of lattice nucleon fields is involved. Using chirally symmetric domain wall fermions, we calculate the proton and the neutron EDFF induced by the CP-violating quark chromo-EDM interaction using the corrected expression. In addition, we calculate the electric dipole moment of the neutron using background electric field that respects time translation invariance and boundary conditions, and find that it decidedly agrees with the new formula but not the old formula for $F_3$. Finally, we analyze some selected lattice results for the nucleon EDM and observe that after the correction is applied, they either agree with zero or are substantially reduced in magnitude, thus reconciling their difference from phenomenological estimates of the nucleon EDM., 26 Jan. 2017
- Refereed, Light flavor-singlet scalars and walking signals in $N_f=8$ QCD on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, Based on the highly improved staggered quark action, we perform lattice simulations of $N_f=8$ QCD and confirm our previous observation of a flavor-singlet scalar meson (denoted as $\sigma$) as light as the pion and various "walking signals" through low-lying spectra, with higher statistics, smaller fermion masses $m_f$, and larger volumes. We measure $M_\pi$, $F_\pi$, $M_\rho$, $M_{a_0}$, $M_{a_1}$, $M_{b_1}$, $M_N$, $M_\sigma$, $F_\sigma$, $\langle \bar{\psi} \psi\rangle$ (both directly and through the GMOR relation), and the string tension. The data are consistent with the spontaneously broken phase of the chiral symmetry, in agreement with the previous results: ratios of the quantities to $M_\pi$ monotonically increase in the smaller $m_f$ region towards the chiral limit similarly to $N_f=4$ QCD, in sharp contrast to $N_f=12$ QCD where the ratios become flattened. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, $\gamma_m \simeq 1$, with a notable exception of $M_\pi$ with $\gamma_m \simeq 0.6$ as in the previous results. This is a salient feature ("walking signal") of $N_f=8$, unlike either $N_f=4$ which has no hyperscaling relation at all, or $N_f=12$ QCD which exhibits universal hyperscaling. We further confirm the previous observation of the light $\sigma$ with mass comparable to the pion in the studied $m_f$ region. In a chiral limit extrapolation of the $\sigma$ mass using the dilaton chiral perturbation theory and also using the simple linear fit, we find the value consistent with the 125 GeV Higgs boson within errors. Our results suggest that the theory could be a good candidate for walking technicolor model, having anomalous dimension $\gamma_m \simeq 1$ and a light flavor-singlet scalar meson as a technidilaton, which can be identified with the 125 GeV composite Higgs in $N_f=8$ one-family model., 22 Oct. 2016
- Refereed, NUCLEAR AND PARTICLE PHYSICS PROCEEDINGS, ELSEVIER SCIENCE BV, Lattice Studies on 8-Flavor QCD in The Light of Physics Beyond The Standard Model, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We report the latest results of the LatKMI collaboration on 8-flavor QCD using Monte Carlo simulations of the lattice gauge theory. The subject receives growing interest with regards to physics beyond the Standard Model (BSM). We show that a flavor-singlet scalar meson (sigma) emerges as one of the lightest bound states and can be a composite Higgs boson with mass 125 GeV. The light sigma may be a technidilaton, a pseudo Nambu-Goldstone boson of the approximate scale symmetry, which results from a slowly running (walking) coupling constant associated with an infra-red fixed point. Consistently to this reasoning, a mass anomalous dimension gamma is found to be large gamma similar to 1. We discuss the applicability of 8-flavor QCD to the BSM model building., Jan. 2016, 270, 242, 246, International conference proceedings
- Refereed, Light composite scalar in eight-flavor QCD on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We present the first observation of a flavor-singlet scalar meson as light as the pion in $N_f=8$ QCD on the lattice, using the Highly Improved Staggered Quark action. Such a light scalar meson can be regarded as a composite Higgs with mass 125 GeV. In accord with our previous lattice results showing that the theory exhibits walking behavior, the light scalar may be a technidilaton, a pseudo Nambu-Goldstone boson of the approximate scale symmetry in walking technicolor., 19 Mar. 2014
- Refereed, Flavor landscape of 10D SYM theory with magnetized extra dimensions, Hiroyuki Abe; Tatsuo Kobayashi; Hiroshi Ohki; Keigo Sumita; Yoshiyuki Tatsuta, We study the flavor landscape of particle physics models based on a ten-dimensional super Yang-Mills theory compactified on magnetized tori preserving four-dimensional ${\cal N}=1$ supersymmetry. Recently, we constructed a semi-realistic model which contains the minimal supersymmetric standard model (MSSM) using an Ansatz of magnetic fluxes and orbifolding projections. However, we can consider more various configurations of magnetic fluxes and orbifolding projections preserving four-dimensional ${\cal N}=1$ supersymmetry. We research systematically such possibilities for leading to MSSM-like models and study their phenomenological aspects., 07 Jul. 2013
- Refereed, Light composite scalar in twelve-flavor QCD on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, Based on lattice simulations using highly improved staggered quarks for twelve-flavor QCD with several bare fermion masses, we observe a flavor-singlet scalar state lighter than the pion in the correlators of fermionic interpolating operators. The same state is also investigated using correlators of gluonic interpolating operators. Combined with our previous study, that showed twelve-flavor QCD to be consistent with being in the conformal window, we infer that the lightness of the scalar state is due to infrared conformality. This result shed some light on the possibility of a light composite Higgs boson ("technidilaton") in walking technicolor theories., 26 May 2013
- Refereed, Walking signals in Nf=8 QCD on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We investigate chiral and conformal properties of the lattice QCD with eight flavors (Nf=8) through meson spectrum using the Highly Improved Staggered Quark (HISQ) action. We also compare our results with those of Nf=12 and Nf=4 which we study on the same systematics. We find that the decay constant F_pi of the pseudoscalar meson "pion" is non-zero, with its mass M_pi consistent with zero, both in the chiral limit extrapolation of the chiral perturbation theory (ChPT). We also measure other quantities which we find are in accord with the pi data results: The rho meson mass is consistent with non-zero in the chiral limit, and so is the chiral condensate, with its value neatly coinciding with that from the Gell-Mann-Oakes-Renner relation in the chiral limit. Thus our data for the Nf=8 QCD are consistent with the spontaneously broken chiral symmetry. Remarkably enough, while the Nf=8 data near the chiral limit are well described by the ChPT, those for the relatively large fermion bare mass m_f away from the chiral limit actually exhibit a finite-size hyperscaling relation, suggesting a large anomalous dimension gamma_m ~ 1. This implies that there exists a remnant of the infrared conformality, and suggests that a typical technicolor ("one-family model") as modeled by the Nf=8 QCD can be a walking technicolor theory having an approximate scale invariance with large anomalous dimension gamma_m ~ 1., 27 Feb. 2013
- Refereed, QUEST FOR THE ORIGIN OF PARTICLES IN THE UNIVERSE, WORLD SCIENTIFIC PUBL CO PTE LTD, KMI Lattice Projecct on 8-Flavor QCD - Explortation of the Walking Technicolor, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We present the report of the LatKMI collaboration on the lattice QCD simulation performed at the KMI computer, "phi", for the cases of 8 flavors, which is expected to be a candidate for the walking technicolor having an approximate scale invariance near the infrared fixed point. The simulation was carried out based on the highly improved staggered quark (HISQ) action. In this proceedings, we report preliminary results on the spectrum, analyzed through the chiral perturbation theory and the finite-size hyperscaling. We observe qualitatively different behavior of the 8-flavor case in contrast to the 4-flavor case which shows clear indication of the hadronic phase as in the usual QCD., 2013, 267, 270, International conference proceedings
- Refereed, QUEST FOR THE ORIGIN OF PARTICLES IN THE UNIVERSE, WORLD SCIENTIFIC PUBL CO PTE LTD, KMI Lattice Project on 16-Flavor QCD, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Aakihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, It is well known that the SU(3) gauge theory with the fundamental 16-flavor fermion is governed by a non-trivial infrared fixed point in the 2-loop perturbation theory, while the theory has not been well investigated by non-perturbative lattice simulations. We investigate properties of 16-flavor QCD by lattice simulation with highly improved action setup (HISQ/tree) at two lattice spacings. We present preliminary results for the mass of the lightest pseudoscalar meson at non-zero fermion mass. We discuss the (finite-size) hyperscaling of our data, the mass anomalous dimension extracted from the scaling, and comparison of the anomalous dimension with the perturbation theory., 2013, 275, 278, International conference proceedings
- Refereed, QUEST FOR THE ORIGIN OF PARTICLES IN THE UNIVERSE, WORLD SCIENTIFIC PUBL CO PTE LTD, Analysis of the Schwinger-Dyson Equation in a box for the Study of Hyperscalling Relations, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We study corrections to the finite-size hyperscaling relation in the conformal window of the large N-f QCD by using the ladder Schwinger-Dyson (SD) equation formulated in a finite space-time with the periodic boundary condition. We find that the anomalous dimension, when identified through the hyperscaling relation neglecting the correction caused by the non-zero fermion mass, yields a value substantially lower than the one at the fixed point for large mass region., 2013, 279, 282, International conference proceedings
- Refereed, QUEST FOR THE ORIGIN OF PARTICLES IN THE UNIVERSE, WORLD SCIENTIFIC PUBL CO PTE LTD, The KMI Lattice Project - Exploring for Technicolor from QCD, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, Investigation of the SU(3) gauge theory with many fermions for the quest for the walking technicolor theory as a KMI project is described. The theory, if it is successfully constructed, can supersede the standard model Higgs sector, and thus can be a candidate of the theory of new physics. We utilize the KMI high-performance computing system phi perform the numerical simulation adopting a state-of-the-art lattice fermion formulation. A hint of the number of fermions for the candidate of the walking technicolor theory is emerging., 2013, 179, 186, International conference proceedings
- Refereed, Phenomenological aspects of 10D SYM theory with magnetized extra dimensions, Hiroyuki Abe; Tatsuo Kobayashi; Hiroshi Ohki; Akane Oikawa; Keigo Sumita, We present a particle physics model based on a ten-dimensional (10D) super Yang-Mills (SYM) theory compactified on magnetized tori preserving four-dimensional ${\cal N}=1$ supersymmetry. The low-energy spectrum contains the minimal supersymmetric standard model with hierarchical Yukawa couplings caused by a wavefunction localization of the chiral matter fields due to the existence of magnetic fluxes, allowing a semi-realistic pattern of the quark and the lepton masses and mixings. We show supersymmetric flavor structures at low energies induced by a moduli-mediated and an anomaly-mediated supersymmetry breaking., 19 Nov. 2012
- Refereed, Nucleon strange quark content from N_f=2+1 lattice QCD with exact chiral symmetry, JLQCD Collaboration; H. Ohki; K. Takeda; S. Aoki; S. Hashimoto; T. Kaneko; H. Matsufuru; J. Noaki; T. Onogi, We calculate the strange quark content of the nucleon in 2+1-flavor lattice QCD. Chirally symmetric overlap fermion formulation is used to avoid the contamination from up and down quark contents due to an operator mixing between strange and light scalar operators, \bar{s}s and \bar{u}u+\bar{d}d. At a lattice spacing a=0.112(1) fm, we perform calculations at four values of degenerate up and down quark masses, which cover a range of the pion mass M_pi \simeq 300-540 MeV. We employ two different methods: one is a direct method where we calculate the strange quark content by directly inserting the strange scalar operator. The other is an indirect method where the quark content is extracted from a derivative of the nucleon mass in terms of the strange quark mass. With these two methods we obtain consistent results with each other. Our best estimate f_{T_s}=0.009(15)(16) is in good agreement with our previous studies in two-flavor QCD., 21 Aug. 2012
- Refereed, Lattice study of conformality in twelve-flavor QCD, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We study infrared conformality of the twelve-flavor QCD on the lattice. Utilizing the highly improved staggered quarks (HISQ) type action which is useful to study the continuum physics, we analyze the lattice data of the mass and the decay constant of a pseudoscalar meson and the mass of a vector meson as well at several values of lattice spacing and fermion mass. Our result is consistent with the conformal hypothesis for the mass anomalous dimension $\gamma_m \sim 0.4-0.5$., 12 Jul. 2012
- Refereed, Lattice study of infrared behaviour in SU(3) gauge theory with twelve massless flavours, C. -J. David Lin; Kenji Ogawa; Hiroshi Ohki; Eigo Shintani, We present details of a lattice study of infrared behaviour in SU(3) gauge theory with twelve massless fermions in the fundamental representation. Using the step-scaling method, we compute the coupling constant in this theory over a large range of scale. The renormalisation scheme in this work is defined by the ratio of Polyakov loops in the directions with different boundary conditions. We closely examine systematic effects, and find that they are dominated by errors arising from the continuum extrapolation. Our investigation suggests that SU(3) gauge theory with twelve flavours contains an infrared fixed point., 28 May 2012
- Refereed, Superfield description of 10D SYM theory with magnetized extra dimensions, Hiroyuki Abe; Tatsuo Kobayashi; Hiroshi Ohki; Keigo Sumita, We present a four-dimensional (4D) ${\cal N}=1$ superfield description of supersymmetric Yang-Mills (SYM) theory in ten-dimensional (10D) spacetime with certain magnetic fluxes in compactified extra dimensions preserving partial ${\cal N}=1$ supersymmetry out of full ${\cal N}=4$. We derive a 4D effective action in ${\cal N}=1$ superspace directly from the 10D superfield action via dimensional reduction, and identify its dependence on dilaton and geometric moduli superfields. A concrete model for three generations of quark and lepton superfields are also shown. Our formulation would be useful for building various phenomenological models based on magnetized SYM theories or D-branes., 24 Apr. 2012
- Refereed, Study of the conformal hyperscaling relation through the Schwinger-Dyson equation, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We study corrections to the conformal hyperscaling relation in the conformal window of the large Nf QCD by using the ladder Schwinger-Dyson (SD) equation as a concrete dynamical model. From the analytical expression of the solution of the ladder SD equation, we identify the form of the leading mass correction to the hyperscaling relation. We find that the anomalous dimension, when identified through the hyperscaling relation neglecting these corrections, yields a value substantially lower than the one at the fixed point \gamma_m^* for large mass region. We further study finite-volume effects on the hyperscaling relation, based on the ladder SD equation in a finite space-time with the periodic boundary condition. We find that the finite-volume corrections on the hyperscaling relation are negligible compared with the mass correction. The anomalous dimension, when identified through the finite-size hyperscaling relation neglecting the mass corrections as is often done in the lattice analyses, yields almost the same value as that in the case of the infinite space-time neglecting the mass correction, i.e., a substantially lower value than \gamma_m^* for large mass. We also apply the finite-volume SD equation to the chiral-symmetry-breaking phase and find that when the theory is close to the critical point such that the dynamically generated mass is much smaller than the explicit breaking mass, the finite-size hyperscaling relation is still operative. We also suggest a concrete form of the modification of the finite-size hyperscaling relation by including the mass correction, which may be useful to analyze the lattice data., 19 Jan. 2012
- Refereed, Spontaneous Parity Violation in SUSY Strong Gauge Theory, Naoyuki Haba; Hiroshi Ohki, We suggest simple models of spontaneous parity violation in supersymmetric strong gauge theory. We focus on left-right symmetric model and investigate vacuum with spontaneous parity violation. Non-perturbative effects are calculable in supersymmetric gauge theory, and we suggest two new models. The first model shows confinement, and the second model has a dual description of the theory. The left-right symmetry breaking and electroweak symmetry breaking are simultaneously occurred with the suitable energy scale hierarchy. The second model also induces spontaneous supersymmetry breaking., 28 Apr. 2011
- Refereed, Non-Abelian Discrete Flavor Symmetries on Orbifolds, Hiroyuki Abe; Kang-Sin Choi; Tatsuo Kobayashi; Hiroshi Ohki; Manabu Sakai, We study non-Abelian flavor symmetries on orbifolds, $S^1/Z_2$ and $T^2/Z_3$. Our extra dimensional models realize $D_N$, $\Sigma(2N^2)$, $\Delta(3N^2)$ and $\Delta(6N^2)$ including $A_4$ and $S_4$. In addition, one can also realize their subgroups such as $Q_N$, $T_7$, etc. The $S_3$ flavor symmetry can be realized on both $S^1/Z_2$ and $T^2/Z_3$ orbifolds., 27 Sep. 2010
- Refereed, Geometric entropy and third order phase transition in d=4 N=2 SYM with flavor, Mitsutoshi Fujita; Hiroshi Ohki, We analyze the phase structure of $d=4$ $\mathcal{N}=2$ large $N$ SYM theory with flavor on $S^1\times S^3$ by using geometric entropy as an order parameter. We introduce chemical potential conjugate to global U(1) symmetry and find the third order phase transition at finite density by using the geometric entropy as the order parameter. We also find that the geometric entropy at the finite density has an interesting behavior at low temperature and for large $N_f$., 02 Jun. 2010
- Refereed, Three-generation Models from E_8 Magnetized Extra Dimensional Theory, Tatsuo Kobayashi; Ryosuke Maruyama; Masaki Murata; Hiroshi Ohki; Manabu Sakai, We study 10D super Yang-Mills E8 theory on the 6D torus compactification with magnetic fluxes. We study systematically the possibilities for realizing 4D supersymmetric standard models with three generations of quarks and leptons. We also study quark mass matrices., 15 Feb. 2010
- Refereed, Flavor structure from magnetic fluxes and non-Abelian Wilson lines, Hiroyuki Abe; Kang-Sin Choi; Tatsuo Kobayashi; Hiroshi Ohki, We study the flavor structure of 4D effective theories, which are derived from extra dimensional theories with magnetic fluxes and non-Abelian Wilson lines. We study zero-mode wavefunctions and compute Yukawa couplings as well as four-point couplings. In our models, we also discuss non-Abelian discrete flavor symmetries such as $D_4$, $\Delta(27)$ and $\Delta(54)$., 12 Jan. 2010
- Refereed, E6,7,8 Magnetized Extra Dimensional Models, Kang-Sin Choi; Tatsuo Kobayashi; Ryosuke Maruyama; Masaki Murata; Yuichiro Nakai; Hiroshi Ohki; Manabu Sakai, We study 10D super Yang-Mills theory with the gauge groups $E_6$, $E_7$ and $E_8$. We consider the torus/orbifold compacfitication with magnetic fluxes and Wilson lines. They lead to 4D interesting models with three families of quarks and leptons, whose profiles in extra dimensions are quasi-localized because of magnetic fluxes., 04 Aug. 2009
- Refereed, Magnetic flux, Wilson line and orbifold, Hiroyuki Abe; Kang-Sin Choi; Tatsuo Kobayashi; Hiroshi Ohki, We study torus/orbifold models with magnetic flux and Wilson line background. The number of zero-modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology., 30 Jul. 2009
- Refereed, Non-Abelian Discrete Flavor Symmetries from Magnetized/Intersecting Brane Models, Hiroyuki Abe; Kang-Sin Choi; Tatsuo Kobayashi; Hiroshi Ohki, We study non-abelian discrete flavor symmetries, which can appear in magnetized brane models. For example, $D_4$, $\Delta(27)$ and $\Delta(54)$ can appear and matter fields with several representations can appear. We also study the orbifold background, where non-abelian flavor symmetries are broken in a certain way., 17 Apr. 2009
- Refereed, Higher Order Couplings in Magnetized Brane Models, Hiroyuki Abe; Kang-Sin Choi; Tatsuo Kobayashi; Hiroshi Ohki, We compute three-point and higher order couplings in magnetized brane models. We show that higher order couplings are written as products of three-point couplings. This behavior is the same as higher order amplitudes by conformal field theory calculations e.g. in intersecting D-brane models., 23 Mar. 2009
- Refereed, A new scheme for the running coupling constant in gauge theories using Wilson loops, Erek Bilgici; Antonino Flachi; Etsuko Itou; Masafumi Kurachi; C. -J David Lin; Hideo Matsufuru; Hiroshi Ohki; Tetsuya Onogi; Takeshi Yamazaki, We propose a new renormalization scheme of the running coupling constant in general gauge theories using the Wilson loops. The renormalized coupling constant is obtained from the Creutz ratio in lattice simulations and the corresponding perturbative coefficient at the leading order. The latter can be calculated by adopting the zeta-function resummation techniques. We perform a benchmark test of our scheme in quenched QCD with the plaquette gauge action. The running of the coupling constant is determined by applying the step-scaling procedure. Using several methods to improve the statistical accuracy, we show that the running coupling constant can be determined in a wide range of energy scales with relatively small number of gauge configurations., 22 Feb. 2009
- Refereed, Three generation magnetized orbifold models, Hiroyuki Abe; Kang-Sin Choi; Tatsuo Kobayashi; Hiroshi Ohki, We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N=1 super Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown., 18 Dec. 2008
- Refereed, Nucleon sigma term and strange quark content from lattice QCD with exact chiral symmetry, H. Ohki; H. Fukaya; S. Hashimoto; T. Kaneko; H. Matsufuru; J. Noaki; T. Onogi; E. Shintani; N. Yamada; for JLQCD Collaboration, We calculate the nucleon sigma term in two-flavor lattice QCD utilizing the Feynman-Hellman theorem. Both sea and valence quarks are described by the overlap fermion formulation, which preserves exact chiral and flavor symmetries on the lattice. We analyse the lattice data for the nucleon mass using the analytical formulae derived from the baryon chiral perturbation theory. From the data at valence quark mass set different from sea quark mass, we may extract the sea quark contribution to the sigma term, which corresponds to the strange quark content. We find that the strange quark content is much smaller than the previous lattice calculations and phenomenological estimates., 29 Jun. 2008
- Refereed, Magnetized orbifold models, Hiroyuki Abe; Tatsuo Kobayashi; Hiroshi Ohki, We study (4+2n)-dimensional N=1 super Yang-Mills theory on the orbifold background with non-vanishing magnetic flux. In particular, we study zero-modes of spinor fields. The flavor structure of our models is different from one in magnetized torus models, and would be interesting in realistic model building., 29 Jun. 2008
- Refereed, Soft supersymmetry breaking terms from D4 x Z2 lepton flavor symmetry, Hajime Ishimori; Tatsuo Kobayashi; Hiroshi Ohki; Yuji Omura; Ryo Takahashi; Morimitsu Tanimoto, We study the supersymmetric model with $D_4 \times Z_2$ lepton flavor symmetry. We evaluate soft supersymmetry breaking terms, i.e. soft slepton masses and A-terms, which are predicted in the $D_4$ flavor model. We consider constraints due to experiments of flavor changing neutral current processes., 06 Mar. 2008
- Refereed, D4 Flavor Symmetry for Neutrino Masses and Mixing, Hajime Ishimori; Tatsuo Kobayashi; Hiroshi Ohki; Yuji Omura; Ryo Takahashi; Morimitsu Tanimoto, We present the $D_4\times Z_2$ flavor symmetry, which is different from the previous work by Grimus and Lavoura. Our model reduces to the standard model in the low energy and there is no FCNC at the tree level. Putting the experimental data, parameters are fixed, and then the implication of our model is discussed. The condition to realize the tri-bimaximal mixing is presented. The possibility for stringy realization of our model is also discussed., 16 Feb. 2008
- Refereed, Determination of B*B pi coupling in unquenched QCD, Hiroshi Ohki; Hideo Matsufuru; Tetsuya Onogi, The $B^* B\pi$ coupling is a fundamental parameter of chiral effective Lagrangian with heavy-light mesons and can constrain the chiral behavior of $f_B$, $B_B$ and the $B\to \pi l \nu$ form factor in the soft pion limit. We compute the $B^* B \pi $ coupling with the static heavy quark and the $O(a)$-improved Wilson light quark. Simulations are carried out with $n_f=2$ unquenched $12^3\times 24$ lattices at $\beta=1.80$ and $16^3\times 32$ lattices at $\beta=1.95$ generated by CP-PACS collaboration. To improve the statistical accuracy, we employ the all-to-all propagator technique and the static quark action with smeared temporal link variables following the quenched study by Negishi {\it et al.}. These methods successfully work also on unquenched lattices, and determine the $B^*B\pi$ coupling with 1--2% statistical accuracy on each lattice spacing., 12 Feb. 2008
- Refereed, GRAND UNIFIED THEORIES: CURRENT STATUS AND FUTURE PROSPECTS, AMER INST PHYSICS, Nucleon sigma term from lattice QCD, Hiroshi Ohki; Tetsuya Onogi, There has been renewed interest in the nucleon sigma term since it determines the neutralino dark matter reaction rate with nucleon through the t-channel Higgs boson exchange. Despite its importance and its long history of theoretical studies, there are still substantial uncertainties. We present our recent studies of the nucleon sigma term based on the JLQCD project of N-f = 2 unquenched lattice QCD simulation with dynamical overlap fermion., 2008, 1015, 52, 66, International conference proceedings
- Refereed, Discrete R-symmetry anomalies in heterotic orbifold models, Takeshi Araki; Kang-Sin Choi; Tatsuo Kobayashi; Jisuke Kubo; Hiroshi Ohki, Anomalies of discrete R-symmetries appearing in heterotic orbifold models are studied. We find that the mixed anomalies for different gauge groups satisfy the universal Green-Schwarz (GS) condition, indicating that these anomalies are canceled by the GS mechanism. An exact relation between the anomaly coefficients of the discrete R-symmetries and one-loop beta-function coefficients is obtained. We also find that the discrete R-symmetries have a good chance to be unbroken down to the supersymmetry breaking scale. Even below this scale a $Z_2$ subgroup is unbroken, which may be an origin of the R-parity of the minimal supersymmetric standard model. Relations between the R-symmetry anomalies and T-duality anomalies are also investigated., 22 May 2007
- Refereed, Non-Factorisable Z2 times Z2 Heterotic Orbifold Models and Yukawa Couplings, Stefan Forste; Tatsuo Kobayashi; Hiroshi Ohki; Kei-jiro Takahashi, We classify compactification lattices for supersymmetric Z2 times Z2 orbifolds. These lattices include factorisable as well as non-factorisable six-tori. Different models lead to different numbers of fixed points/tori. A lower bound on the number of fixed tori per twisted sector is given by four, whereas an upper bound consists of 16 fixed tori per twisted sector. Thus, these models have a variety of generation numbers. For example, in the standard embedding, the smallest number of net generations among these classes of models is equal to six, while the largest number is 48. Conditions for allowed Wilson lines and Yukawa couplings are derived., 06 Dec. 2006
- Refereed, Journal of High Energy Physics, Springer Science and Business Media LLC, Modular origin of mass hierarchy: Froggatt-Nielsen like mechanism, Hitomi Kuranaga; Hiroshi Ohki; Shohei Uemura, Abstract We study Froggatt-Nielsen (FN) like flavor models with modular symmetry. The FN mechanism is a convincing solution to the flavor puzzle in the quark sector. The FN mechanism requires an extra U(1) gauge symmetry which is broken at high energies. Alternatively, in the framework of modular symmetry the modular weights can play the role of the FN charges of the extra U(1) symmetry. Based on the FN-like mechanism with modular symmetry we present new flavor models for the quark sector. Assuming that the three generations have a common representation under the modular symmetry, our models simply reproduce the FN-like Yukawa matrices. We also show that the realistic mass hierarchy and mixing angles, which are related to each other through the modular parameters and a scalar vev, can be realized in models with several finite modular groups (and their double covering groups) without unnatural hierarchical parameters., Jul. 2021, 2021, 7, Scientific journal

- 1月 2021, 1, 9
- Refereed, 0月 2021, 1, 8
- Not Refereed, Proceedings of 37th International Symposium on Lattice Field Theory — PoS(LATTICE2019), Sissa Medialab, Computing Nucleon Electric Dipole Moment from lattice QCD, Hiroshi Ohki; Taku Izubuchi; Sergey Syritsyn, 22 Apr. 2020, 363, 290, 0, 14, Introduction international proceedings, True
- Not Refereed, Calculation of Nucleon Electric Dipole Moments Induced by Quark Chromo-Electric Dipole Moments and the QCD $θ$-term, S. Syritsyn; T. Izubuchi; H. Ohki, Electric dipole moments (EDMs) of nucleons and nuclei, which are sought as evidence of CP violation, require lattice calculations to connect constraints from experiments to limits on the strong CP violation within QCD or CP violation introduced by new physics from beyond the standard model. Nucleon EDM calculations on a lattice are notoriously hard due to large statistical noise, chiral symmetry violating effects, and potential mixing of the EDM and the anomalous magnetic moment of the nucleon. In this report, details of ongoing lattice calculations of proton and neutron EDMs induced by the QCD $\theta$-term and the quark chromo-EDM, the lowest-dimension effective CP-violating quark-gluon interaction are presented. Our calculation employs chiral-symmetric fermion discretization. An assessment of feasibility of nucleon EDM calculations at the physical point is discussed., 16 Jan. 2019
- Not Refereed, Progress in the Nucleon Electric Dipole Moment Calculations in Lattice QCD, S. Syritsyn; T. Izubuchi; H. Ohki, Electric dipole moments (EDMs), which are sought as evidence of CP violation, require lattice calculations to connect constraints from experiments to limits on the strong CP violation within QCD or CP violation in new physics beyond the standard model. Nucleon EDM calculations on a lattice are notoriously hard due to large statistical noise, chiral symmetry violating effects, and potential mixing of the EDM and the anomalous magnetic moment of the nucleon. In this report, details of ongoing lattice calculations of proton and neutron EDMs induced by the QCD $\theta$-term and the quark chromo-EDM, the lowest-dimension effective CP-violating quark-gluon interaction are presented. Our calculation employs chiral-symmetric fermion discretization. An assessment of feasibility of nucleon EDM calculations at the physical point is discussed., 08 Oct. 2018
- Not Refereed, Flavor-singlet spectrum in multi-flavor QCD, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes., 18 Oct. 2017
- Not Refereed, Calculation of Nucleon Electric Dipole Moments Induced by Quark Chromo-Electric Dipole Moments, Taku Izubuchi; Michael Abramczyk; Tom Blum; Hiroshi Ohki; Sergey Syritsyn, We present initial results of computing nucleon electric dipole moment induced by quark chromo-EDM, CP-violating quark-gluon coupling. Using chirally-symmetric domain wall and M\"obius fermions with pion mass $m_\pi=172\text{ MeV}$, we calculate the connected part of the electric dipole form factor $F_3(Q^2)$. In addition, we perform an exploratory study of the method to calculate EDM using uniform background electric field on a lattice introduced without breaking the periodicity in the time direction., 31 Jan. 2017
- Not Refereed, MODERN PHYSICS LETTERS A, WORLD SCIENTIFIC PUBL CO PTE LTD, Determinations of V-us using inclusive hadronic tau decay data, Kim Maltman; Renwick James Hudspith; Randy Lewis; Taku Izubuchi; Hiroshi Ohki; James M. Zanotti, Two methods for determining |V-us| employing inclusive hadronic tau decay data are discussed. The first is the conventional flavor-breaking sum rule determination whose usual implementation produces results similar to 3 sigma low compared to three-family unitary expectations. The second is a novel approach combining experimental strange hadronic tau distributions with lattice light-strange current-current two-point function data. Preliminary explorations of the latter show the method promises |V-us| determinations competitive with those from K-l3 and Gamma[K-mu 2]/Gamma[(mu 2)]. For the former, systematic issues in the conventional implementation are investigated. Unphysical dependences of |V-us| on the choice of sum rule weight, w, and upper limit, s(0), of the weighted experimental spectral integrals are observed, the source of these problems identified and a new implementation which overcomes these problems developed. Lattice results are shown to provide a tool for quantitatively assessing truncation uncertainties for the slowly converging D = 2 OPE series. The results for |V-us| from this new implementation are shown to be free of unphysical w- and s(0)-dependences, and similar to 0.0020 higher than those produced by the conventional implementation. With preliminary new K pi branching fraction results as input, we find |V-us| in excellent agreement with that obtained from K-l3, and compatible within errors with expectations from three-family unitarity., Sep. 2016, 31, 29, Book review
- Not Refereed, Dark Side of the Standard Model: Dormant New Physics Awaken, Shinya Matsuzaki; Hiroshi Ohki; Koichi Yamawaki, We find that the nonperturbative physics of the standard-model Higgs Lagrangian provides a dark matter candidate, "dormant skyrmion in the standard model", the same type of the skyrmion, a soliton, as in the hadron physics. It is stabilized by another nonperturbative object in the standard model, the dynamical gauge boson of the hidden local symmetry, which is also an analogue of the rho meson., 12 Aug. 2016
- Not Refereed, S-parameter and vector decay constant in QCD with eight fundamental fermions, LatKMI collaboration; Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, SU(3) gauge theory with eight massless fundamental fermions seems to be near the conformal boundary, and is a candidate theory of walking technicolor. Along the series of study by LatKMI collaboration using HISQ fermions, S-parameter and vector decay constant, which provide important constraints in the model of electroweak symmetry breaking, are calculated for this theory. Use of various volumes allows a systematic investigation of finite volume effects. A strong sensitivity of the S-parameter to the volume is found., 02 Feb. 2016
- Not Refereed, Topological observables in many-flavour QCD, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, SU(3) gauge theory with eight massless flavours is believed to be walking, while the corresponding twelve- and four-flavour appear IR-conformal and confining respectively. Looking at the simulations performed by the LatKMI collaboration of these theories, we use the topological susceptibility as an additional probe of the IR dynamics. By drawing a comparison with SU(3) pure gauge theory, we see a dynamical quenching effect emerge at larger number of flavours, which is suggestive of emerging near-conformal and conformal behaviour., 18 Jan. 2016
- Not Refereed, Walking and conformal dynamics in many-flavor QCD, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihito Shibata; Koichi Yamawaki; Takeshi Yamazaki, In the search for a realistic walking technicolor model, QCD with many flavors is an attractive candidate. From the series of studies by the LatKMI collaboration, we present updated results of the scaling properties of various hadron spectra, including the (pseudo)scalar, vector, and baryon channels, for $N_f=8$ QCD analyzed with the HISQ action. By comparing these with $N_f=12$ QCD, which has properties consistent with conformality, possible signals of walking dynamics are discussed. We also present a preliminary result of the flavor-singlet pseudoscalar mass in many-flavor QCD., 11 Jan. 2016
- Not Refereed, SU(3) gauge theory with four degenerate fundamental fermions on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, As a part of the project studying large $N_f$ QCD, the LatKMI Collaboration has been investigating the SU(3) gauge theory with four fundamental fermions (four-flavor QCD). The main purpose of studying four-flavor QCD is to provide a qualitative comparison to $N_f= 8$, $12$, $16$ QCD; however, a quantitative comparison to real-world QCD is also interesting. To make such comparisons more meaningful, it is desirable to use the same kind of lattice action consistently, so that qualitative difference of different theories are less affected by artifacts of lattice discretization. Here, we adopt the highly-improved staggered quark action with the tree-level Symanzik gauge action (HISQ/tree), which is exactly the same as the setup for our simulations for $SU(3)$ gauge theories with $N_f=8$, $12$ and $16$ fundamental fermions~\cite{Aoki:2013xza, Aoki:2012eq, Aoki:2014oma}. In the next section, we show the fermion mass dependence of $F_\pi$, $\langle\bar{\psi}\psi\rangle$, $M_\pi$, $M_\rho$, $M_N$ and their chiral extrapolations. In section 3, preliminary results of the measurement of the mass of the flavor-singlet scalar bound state will be reported., 03 Dec. 2015
- Not Refereed, Nucleon axial and tensor charges with dynamical overlap quarks, N. Yamanaka; H. Ohki; S. Hashimoto; T. Kaneko, We report on our calculation of the nucleon axial and tensor charges in 2+1-flavor QCD with dynamical overlap quarks. Gauge ensembles are generated at a single lattice spacing 0.12 fm and at a strange quark mass close to its physical value. We employ the all-mode-averaging technique to calculate the relevant nucleon correlation functions, and the disconnected quark loop is efficiently calculated by using the all-to-all quark propagator. We present our preliminary results for the isoscalar and isovector charges obtained at pion masses $m_\pi$ = 450 and 540 MeV., 14 Nov. 2015
- Not Refereed, Lattice study for conformal windows of SU(2) and SU(3) gauge theories with fundamental fermions, Cynthia Y. -H. Huang; Issaku Kanamori; C. -J. David Lin; Kenji Ogawa; Hiroshi Ohki; Alberto Ramos; Enrico Rinaldi, We present our investigation of SU(2) gauge theory with 8 flavours, and SU(3) gauge theory with 12 flavours. For the SU(2) case, at strong bare coupling, $\beta \lesssim 1.45$, the distribution of the lowest eigenvalue of the Dirac operator can be described by chiral random matrix theory for the Gaussian symplectic ensemble. Our preliminary result indicates that the chiral phase transition in this theory is of bulk nature. For the SU(3) theory, we use high-precision lattice data to perform the step-scaling study of the coupling, $g_{ { \rm GF } }$, in the Gradient Flow scheme. We carefully examine the reliability of the continuum extrapolation in the analysis, and conclude that the scaling behaviour of this SU(3) theory is not governed by possible infrared conformality at $g_{ { \rm GF } }^{2} \lesssim 6$., 06 Nov. 2015
- Not Refereed, Lattice study of the scalar and baryon spectra in many-flavor QCD, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, In the search for a composite Higgs boson in walking technicolor models, many flavor QCD, in particular with $N_f=8$, is an attractive candidate, and has been found to have a composite flavor-singlet scalar as light as the pion. Based on lattice simulations of this theory with the HISQ action, we will present our preliminary results on the scalar decay constant using the fermionic bilinear operator, and on the mass of the lightest baryon state which could be a dark matter candidate. Combining these two results, implications for dark matter direct detection are also discussed., 26 Oct. 2015
- Not Refereed, Topological insights in many-flavor QCD on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, LatKMI Collaboration discusses the topological insights in many-flavor QCD on the lattice. We explore walking/conformal/confining phase in $N_\mathrm{f}$ = 4, 8 and 12 (in particular $N_\mathrm{f}$ = 8) lattice QCD via the topological charge and susceptibility, eigenvalues and anomalous dimension., 20 Oct. 2015
- Not Refereed, Conformality in twelve-flavour QCD, Yasumichi Aoki; Tatsumi Aoyama; Ed Bennett; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, The spectrum of twelve-flavor QCD has been studied in details by the LatKMI collaboration. In this proceeding we present our updated results for the spectrum obtained with the HISQ action at two lattice spacings, several volumes and fermion masses. In particular, we emphasize the existence of a flavor-singlet scalar state parametrically light with respect to the rest of the spectrum, first reported in our paper. This feature is expected to be present for theories in the conformal window, but the lattice calculation of such a state is difficult and requires noise-reduction techniques together with large statistics, in order to evaluate disconnected diagrams. Being able to provide a robust observed connection between a light flavor-singlet scalar and (near-)conformality is an important step towards observing a light composite Higgs boson in walking technicolor theories on the lattice. We also show updated results for the mass anomalous dimension $\gamma_m$ obtained from various spectral quantities, including the string tension, under the assumption that the theory is inside the conformal window., 27 Jan. 2015
- Not Refereed, Phase Structure Study of SU(2) Lattice Gauge Theory with 8 Flavors, Cynthia Y. -H. Huang; C. -J. David Lin; Kenji Ogawa; Hiroshi Ohki; Enrico Rinaldi, We present the investigation of the strong bare-coupling regime of SU(2) lattice gauge theory with 8 fermion flavors in the fundamental representation. The simulations are performed with unimproved staggered fermions and the plaquette gauge action. One bulk phase transition is observed through the measurement of the plaquette. The results of cold-start and hot-start simulations, as well as the hysteresis study, indicate the order of this transition can be weakly first order. Using the smeared Polyakov loops, and a method inspired by the constraint effective potential, we study the vacuum structure near the confining-deconfining phase transition. The Dirac operator eigenvalue spectrum is investigated, where further analysis is needed to clarify the properties of the chiral phase structure., 31 Oct. 2014
- Not Refereed, SU(3) gauge theory with 12 flavours in a twisted box, C. -J. David Lin; Kenji Ogawa; Hiroshi Ohki; Alberto Ramos; Eigo Shintani, We present preliminary result for the step-scaling study of the coupling constant with the Yang-Mills gradient flow, in the twelve-favour SU(3) gauge theory. In this work, the lattice simulation is performed using unimproved staggered fermions and the Wilson plaquette gauge action, from which the gradient flow is also implemented. Imposing twisted boundary condition a'la t'Hooft and Parisi, our calculation is performed at zero fermion mass. The renormalised coupling constant is extracted via the computation of the energy density. In order to examine the reliability of the continuum extrapolation, we investigate this coupling constant using two different lattice discretisations. Our result shows that in order to control the systematic effects in the continuum extrapolation, it is necessary to implement a large enough gradient-flow time. In the current calculation, the gauge-field averaging radius corresponding to the flow time has to be as large as 40% of the lattice size., 31 Oct. 2014
- Not Refereed, JOURNAL OF HIGH ENERGY PHYSICS, SPRINGER, Non-Abelian discrete flavor symmetries of 10D SYM theory with magnetized extra dimensions, Hiroyuki Abe; Tatsuo Kobayashi; Hiroshi Ohki; Keigo Sumita; Yoshiyuki Tatsuta, We study discrete flavor symmetries of the models based on a ten-dimensional supersymmetric Yang-Mills (10D SYM) theory compactified on magnetized tori. We assume non-vanishing non-factorizable fluxes as well as the orbifold projections. These setups allow model-building with more various flavor structures. Indeed, we show that there exist various classes of non-Abelian discrete flavor symmetries. In particular, we find that S-3 flavor symmetries can be realized in the framework of the magnetized 10D SYM theory for the first time., Jun. 2014, 6, Technical report
- Not Refereed, Composite flavor-singlet scalar in twelve-flavor QCD, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We report the calculation of the flavor-singlet scalar in the SU(3) gauge theory with the degenerate twelve fermions in the fundamental representation using a HISQ-type action at a fixed $\beta$. In order to reduce the large statistical error coming from the vacuum-subtracted disconnected correlator, we employ a noise reduction method and a large number of configurations. We observe that the flavor-singlet scalar is lighter than the pion in this theory from the calculations with the fermion bilinear and gluonic operators. This peculiar feature is considered to be due to the infrared conformality of this theory, and it is a promissing signal for a walking technicolor, where a light composite Higgs boson is expected to emerge by approximate conformal dynamics., 27 Nov. 2013
- Not Refereed, Gluonic observables and the scalar spectrum of twelve-flavour QCD, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We measure glueball masses and the string tension in twelve-flavour QCD, aiming at comparing the emerging gluonic spectrum to the mesonic one. When approaching the critical surface at zero quark mass, the hierarchy of masses in the different sectors of the spectrum gives a new handle to determine the existence of an infrared fixed point. We describe the details of our gluonic measurements and the results obtained on a large number of gauge configurations generated with the HISQ action. In particular, we focus on the scalar glueball and its mixing with a flavour-singlet fermionic state, which is lighter than the pseudoscalar (would-be pion) state. The results are interesting in view of a light composite Higgs boson in walking technicolor theories., 03 Oct. 2013
- Not Refereed, A light composite scalar in eight-flavor QCD on the lattice, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kohtaroh Miura; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, In search for a composite Higgs boson (techni-dilaton) in the walking technicolor, we present our preliminary results on the first observation of a light flavor-singlet scalar in a candidate theory for the walking technicolor, the Nf=8 QCD, which was found in our previous paper to have spontaneous chiral symmetry breaking together with remnants of the conformality. Based on simulations with the HISQ-type action on several lattice sizes with various fermion masses, we find evidence of a flavor-singlet scalar meson with mass comparable to that of the Nambu-Goldstone pion in both the small fermion-mass region, where chiral perturbation theory works, and the intermediate fermion-mass region where the hyperscaling relation holds. We further discuss its chiral limit extrapolation in comparison with other states studied in our previous paper: the scalar has a mass much smaller than that of the vector meson, which is compared to the Nambu-Goldstone pion having a vanishing mass in that limit., 03 Sep. 2013
- Not Refereed, The scalar spectrum of many-flavour QCD, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Enrico Rinaldi; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, The LatKMI collaboration is studying systematically the dynamical properties of N_f = 4,8,12,16 SU(3) gauge theories using lattice simulations with (HISQ) staggered fermions. Exploring the spectrum of many-flavour QCD, and its scaling near the chiral limit, is mandatory in order to establish if one of these models realises the Walking Technicolor scenario. Although lattice technologies to study the mesonic spectrum are well developed, scalar flavour-singlet states still require extra effort to be determined. In addition, gluonic observables usually require large-statistic simulations and powerful noise-reduction techniques. In the following, we present useful spectroscopic methods to investigate scalar glueballs and scalar flavour-singlet mesons, together with the current status of the scalar spectrum in N_f = 12 QCD from the LatKMI collaboration., 19 Feb. 2013
- Not Refereed, Exploring walking behavior in SU(3) gauge theory with 4 and 8 HISQ quarks, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We present the report of the LatKMI collaboration on the lattice QCD simulation for the cases of 4 and 8 flavors. The Nf=8 in particular is interesting from the model-building point of view: The typical walking technicolor model with the large anomalous dimension is the so-called one-family model (Farhi-Susskind model). Thus we explore the walking behavior in LQCD with 8 HISQ quarks by comparing with the 4-flavor case (in which the chiral symmetry is spontaneously broken). We report preliminary results on the spectrum, analyzed through the chiral perturbation theory and the finite-size hyperscaling, and we discuss the availability of the Nf=8 QCD to the phenomenology., 15 Jan. 2013
- Not Refereed, Low energy spectra in many flavor QCD with Nf=12 and 16, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We present our result of the many-flavor QCD. Information of the phase structure of many-flavor SU(3) gauge theory is of great interest, since the gauge theories with the walking behavior near the infrared fixed point are candidates of new physics for the origin of the dynamical electroweak symmetry breaking. We study the SU(3) gauge theories with 12 and 16 fundamental fermions. Utilizing the HISQ type action which is useful to study the continuum physics, we analyze the lattice data of the mass and the decay constant of the pseudoscalar meson and the mass of the vector meson as well at several values of lattice spacing and fermion mass. The finite size scaling test in the conformal hypothesis is also performed. Our data is consistent with the conformal scenario for Nf=12. We obtain the mass anomalous dimension $\gamma_m \sim 0.4-0.5$. An update of $N_f=16$ study is also shown., 28 Nov. 2012
- Not Refereed, Many flavor QCD with N_f=12 and 16, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, Information of the phase structure of many flavor SU(3) gauge theory is of great interest for finding a theory which dynamically breaks the electro-weak symmetry. We study the SU(3) gauge theory with fermions for $N_f=12$ and 16 in fundamental representation. Both of them, through perturbation theory, reside in the conformal phase. We try to determine the phase of each theory non-perturbatively with lattice simulation and to find the characteristic behavior of the physical quantities in the phase. HISQ type staggered fermions are used to reduce the discretization error which could compromise the behavior of the physical quantity to determine the phase structure at non-zero lattice spacings. Spectral quantities such as bound state masses of meson channel and meson decay constants are investigated with careful finite volume analysis. Our data favor the conformal over chiral symmetry breaking scenario for both $N_f=12$ and 16., 22 Feb. 2012
- Not Refereed, Many flavor QCD as exploration of the walking behavior with the approximate IR fixed point, Yasumichi Aoki; Tatsumi Aoyama; Masafumi Kurachi; Toshihide Maskawa; Kei-ichi Nagai; Hiroshi Ohki; Akihiro Shibata; Koichi Yamawaki; Takeshi Yamazaki, We present the first report of the LatKMI collaboration on the the lattice QCD simulation performed at the KMI computer, "$\varphi$", for the cases of 4 flavors and 8 flavors, the latter being expected to be a candidate for the walking technicolor having an approximate scale invariance near the infrared fixed point. The simulation was carried out based on the highly improved staggered quark (HISQ) action. In this proceedings, we report preliminary results on the spectrum, analyzed through the chiral perturbation theory and the finite-size hyperscaling. We observe qualitatively different behavior of the 8-flavor case in contrast to the 4-flavor case which shows clear indication of the hadronic phase as in the usual QCD., 21 Feb. 2012
- Not Refereed, The Infrared behavior of SU(3) Nf=12 gauge theory -about the existence of conformal fixed point-, Kenji Ogawa; Tatsumi Aoyama; Hiroaki Ikeda; Etsuko Itou; Masafumi Kurachi; C. -J. David Lin; Hideo Matsufuru; Hiroshi Ohki; Tetsuya Onogi; Eigo Shintani; Takeshi Yamazaki, Incorporated with twisted boundary condition, Polyakov loop correlators can give a definition of the renormalized coupling. We employ this scheme for the step scaling method (with step size s = 2) in the search of conformal fixed point of SU(3) gauge theory with 12 massless flavors. Staggered fermion and plaquette gauge action are used in the lattice simulation with six different lattice sizes, L/a = 20, 16, 12, 10, 8 and 6. For the largest lattice size, L/a = 20, we used a large number of Graphics Processing Units (GPUs) and accumulated 3,000,000 trajectories in total. We found that the step scaling function sigma (u) is consistent with u in the low-energy region. This means the existence of conformal fixed point. Some details of our analysis and simulations will also be presented., 07 Nov. 2011
- Not Refereed, Conformal fixed point of SU(3) gauge theory with 12 fundamental fermions, Tatsumi Aoyama; Hiroaki Ikeda; Masafumi Kurachi; C. -J; David Lin; Hideo Matsufuru; Kenji Ogawa; Hiroshi Ohki; Tetsuya Onogi; Eigo Shintani; Takeshi Yamazaki, We study the infrared properties of SU(3) gauge theory coupled to 12 massless

Dirac fermions in the fundamental representation. The renormalized running

coupling constant is calculated in the Twisted Polyakov loop scheme on the

lattice. From the step-scaling analysis, we find that the infrared behavior of

the theory is governed by a non-trivial fixed point., 27 Sep. 2011, Technical report - Not Refereed, Search for the IR fixed point in the Twisted Polyakov Loop scheme (II), Etsuko Itou; Tatsumi Aoyama; Masafumi Kurachi; C. -J. David Lin; Hideo Matsufuru; Hiroshi Ohki; Tetsuya Onogi; Eigo Shintani; Takeshi Yamazaki, We measure the renormalized coupling in the Twisted Polyakov loop scheme for SU(3) gauge theory coupled with $N_f=12$ fundamental fermions. To find the infrared fixed point of this theory, we focus on the step scaling function for the renormalized coupling. We take the continuum limit using the linear function of $(a/L)^2$ and a constant fit function. We find that there is a sizeable systematic error due to the choice of the continuum extrapolation function in the low energy region. We will give some directions to reduce the systematic errors., 02 Nov. 2010
- Not Refereed, Study of the scaling properties in SU(2) gauge theory with eight flavors, Hiroshi Ohki; Tatsumi Aoyama; Etsuko Itou; Masafumi Kurachi; C. -J. David Lin; Hideo Matsufuru; Tetsuya Onogi; Eigo Shintani; Takeshi Yamazaki, We present our preliminary study of the SU(2) gauge theory with 8 flavors of fermions in fundamental representation. This theory could be a candidate of the gauge theory with conformal fixed point. By using Wilson/Polyakov loop in a finite volume with twisted boundary conditions, we study the renormalization group flow of the gauge coupling constant. Our calculation gives consistent result with the perturbative prediction of the running coupling in the weak coupling region. We investigate a possible signal for conformal behavior in the strong coupling region., 01 Nov. 2010
- Not Refereed, Chiral four dimensional field theory from superstring and higher dimensional super Yang-Mills theory, Hiroshi Ohki, We study four dimensional field theory from the low-energy effective theory of Type I, II or heterotic string theories. Chiral fermions in four dimensions are obtained by several mechanisms. Especially, the background flux is one of the most interesting mechanisms for obtaining four dimensional chiral theories. Chiral matter fields have localized wavefunctions on extra dimensions. We discuss about the relations between background flux and low-energy spectra which are counted by their zero-modes. Yukawa couplings are free parameters in the standard model and may be related to the underlying physics. In the string theory or its low-energy limit, they are determined by overlap integral of wavefunctions on extra dimensions. We also study the higher order couplings based on the field theoretical approach. From the analysis of generic n-point couplings, we can discuss about flavor structures. We find that in such a construction some discrete flavor symmetries appear in the four dimensional effective theory. Their phenomenological implications are discussed. Furthermore we extend these constructions to orbifold background. Magnetic flux still plays an important role and leads to various types of low-energy spectra different from that of toroidal compactifications. The orbifold models with heterotic string are also investigated., 26 Mar. 2010
- Not Refereed, Non-Abelian Discrete Symmetries in Particle Physics, Hajime Ishimori; Tatsuo Kobayashi; Hiroshi Ohki; Hiroshi Okada; Yusuke Shimizu; Morimitsu Tanimoto, We review pedagogically non-Abelian discrete groups, which play an important role in the particle physics. We show group-theoretical aspects for many concrete groups, such as representations, their tensor products. We explain how to derive, conjugacy classes, characters, representations, and tensor products for these groups (with a finite number). We discussed them explicitly for $S_N$, $A_N$, $T'$, $D_N$, $Q_N$, $\Sigma(2N^2)$, $\Delta(3N^2)$, $T_7$, $\Sigma(3N^3)$ and $\Delta(6N^2)$, which have been applied for model building in the particle physics. We also present typical flavor models by using $A_4$, $S_4$, and $\Delta (54)$ groups. Breaking patterns of discrete groups and decompositions of multiplets are important for applications of the non-Abelian discrete symmetry. We discuss these breaking patterns of the non-Abelian discrete group, which are a powerful tool for model buildings. We also review briefly about anomalies of non-Abelian discrete symmetries by using the path integral approach., 18 Mar. 2010
- Not Refereed, Search for the IR fixed point in the twisted Polyakov loop scheme, Erek Bilgici; Antonino Flachi; Etsuko Itou; Masafumi Kurachi; C. -J. David Lin; Hideo Matsufuru; Hiroshi Ohki; Tetsuya Onogi; Eigo Shintani; Takeshi Yamazaki, We present a non-perturbative study of the running coupling constant in the Twisted Polyakov Loop (TPL) scheme. We investigate how the systematic and statistical errors can be controlled {\it via} a feasibility study in SU(3) pure Yang-Mills theory. We show that our method reproduces the perturbative determination of the running coupling in the UV. In addition, our numerical result agrees with the theoretical prediction of this coupling constant in the IR. We also present our preliminary results for $N_f=12$ QCD, where an IR fixed point may be present., 21 Oct. 2009
- Not Refereed, Nucleon sigma term and strange quark content in 2+1-flavor QCD with dynamical overlap fermions, H. Ohki; S. Aoki; H. Fukaya; S. Hashimoto; T. Kaneko; H. Matsufuru; J. Noaki; T. Onogi; E. Shintani; N. Yamada, We study the sigma term and the strange quark content of nucleon in 2+1-flavor QCD with dynamical overlap fermions. We analyze the lattice data of nucleon mass taken at two different strange quark masses with five values of up and down quark masses each. Using the reweighting technique, we study the strange quark mass dependence of the nucleon and extract the strange quark content., 17 Oct. 2009
- Not Refereed, Calculation of the nucleon sigma term and strange quark content with two flavors of dynamical overlap fermions, H. Ohki; H. Fukaya; S. Hashimoto; H. Matsufuru; J. Noaki; T. Onogi; E. Shintani; N. Yamada, We present a calculation of the nucleon sigma term on two-flavor QCD configurations with dynamical overlap fermions. We analyse the lattice data for the nucleon mass using the baryon chiral perturbation theory. Using partially quenched data sets, we extract the connected and disconnected contributions to the nucleon sigma term separately. Chiral symmetry on the lattice simplifies the determination of the disconnected contribution. We find that the strange quark content, which determines the neutralino dark matter reaction rate with nucleon through the Higgs boson exchange, is much smaller than the previous lattice results., 23 Oct. 2008
- Not Refereed, A New Method of Calculating the Running Coupling Constant, Erek Bilgici; Antonino Flachi; Etsuko Itou; Masafumi Kurachi; C. -J David Lin; Hideo Matsufuru; Hiroshi Ohki; Tetsuya Onogi; Takeshi Yamazaki, We propose a new method to compute the running coupling constant of gauge theories on the lattice. We first give the definition of the running coupling in the new scheme using the Wilson loops in a finite volume, and explain how the running of the coupling constant is extracted from the measurement of the volume dependence. The perturbative calculation of the renormalization constant to define the scheme is also given at the leading order. As a benchmark test of the new scheme we apply the method the case of the quenched QCD. We show the preliminary result from our numerical simulations which are carried out with plaquette gauge action for various lattice sizes and bare lattice couplings. With techniques to improve the statistical accuracy, we show that we can determine the non-perturbative running of the coupling constant in a wide range of the energy scale with relatively small number of gauge configurations in our scheme. We compare our lattice data of the running coupling constant with perturbative renormalization group evolution at one- and two-loop order, and confirm the consistency between them at high energy., 21 Aug. 2008
- Not Refereed, High precision study of B*B pi coupling in unquenched QCD, Hiroshi Ohki; Hideo Matsufuru; Tetsuya Onogi, The B* B pi coupling is a fundamental parameter of chiral effective Lagrangian with heavy-light mesons and can constrain the B->pi l nu form factor in the soft pion limit which will be useful for precise determination of |Vub|. We compute the B* B pi coupling with the static heavy quark and the O(a)-improved Wilson light quark. Simulations are carried out with n_f=2 unquenched 12^3x24 lattices at beta=1.80 generated by CP-PACS collaboration. Following the quenched study by Negishi et al., we employ the all-to-all propagator with 200 low eigenmodes as well as HYP smeared link to improve the statistical accuracy., 02 Nov. 2007

- 978-3-662-64679-3
- 物理科学,この1年 2020, 丸善出版, パリティ編集委員会, 物質優勢宇宙のなぞと格子量子色力学, 2020, vi, 157p, 9784621304860, 26365944, cinii_books;rm:research_project_id
- An Introduction to Non-Abelian Discrete Symmetries for Particle Physicists, Springer, Hajime Ishimori; Tatsuo Kobayashi; Hiroshi Ohki; Hiroshi Okada; Yusuke Shimizu; Morimitsu Tanimoto, 2012
- An introduction to non-Abelian discrete symmetries for particle physicists (Second Edition), Springer, Kobayashi, Tatsuo; Ohki, Hiroshi; Okada, Hiroshi; Shimizu, Yusuke; Tanimoto, Morimitsu, Jan. 2022, xii, 353 p., 9783662646793

- Oral presentation, 14 Sep. 2021, 17 Sep. 2021
- Public discourse, 15 Nov. 2021, 15 Nov. 2021
- Oral presentation, 26 Jul. 2021, 30 Jul. 2021
- 14 Sep. 2020, 17 Sep. 2020
- Oral presentation, 12 Mar. 2021, 15 Mar. 2021
- Hiroshi Ohki, 2019 Lattice X Intensity Frontier Workshop, Calculation of Electric Dipole Moments of the Nucleon, 23 Sep. 2019, 23 Sep. 2019, 25 Sep. 2019
- Hiroshi Ohki, The 37th International Symposium on Lattice Field Theory, Computing Nucleon Electric Dipole Moments from Lattice QCD, 20 Jun. 2019, 16 Jun. 2019, 22 Jun. 2019
- Hiroshi Ohki, International Molecule-type Workshop Frontiers in Lattice QCD and related topics, Computing Nucleon Electric Dipole Moments in Lattice QCD, 26 Apr. 2019, 15 Apr. 2019, 26 Apr. 2019
- Hiroshi Ohki, The 24th Regular Meeting of the New Higgs Working Group, Gravitational Waves from Walking Technicolor, 22 Dec. 2018, 21 Dec. 2018, 22 Dec. 2018
- Hiroshi Ohki, Progress in Particle Physics 2018, Nucleon Electric Dipole Moments from Lattice QCD, 09 Aug. 2018, 06 Aug. 2018, 10 Aug. 2018
- Hiroshi Ohki, 10 th International Workshop on Fundamental Physics Using Atoms (FPUA), Nucleon Electric Dipole Moments from Lattice QCD, 08 Jan. 2018, 08 Jan. 2018, 09 Jan. 2018
- Hiroshi Ohki, The 7th KIAS Workshop on Particle Physics and Cosmology and The 2nd KEK-NCTS-KIAS Workshop on Particle Physics Phenomenology, Nucleon Electric Dipole Moments from Lattice QCD, 10 Nov. 2017, 06 Nov. 2017, 10 Nov. 2017
- Hiroshi Ohki, The Physical Society of Japan 2017 Autumn Meeting, Nucleon structure and physics beyond the SM, 14 Sep. 2017, 12 Sep. 2017, 15 Sep. 2017
- Hiroshi Ohki, 35th International Symposium On Lattice Field Theory, |Vus| determination from inclusive strange tau decay and lattice HVP, 23 Jun. 2017, 18 Jun. 2017, 24 Jun. 2017
- Hiroshi Ohki, The Physical Society of Japan 2017 Annual Meeting, Lattice calculation of quark-chromo EDM, 19 Mar. 2017, 17 Mar. 2017, 20 Mar. 2017
- Hiroshi Ohki, The international workshop on future potential of high intensity accelerators for particle and nuclear physics (HINT2016), Determination of |Vus| from hadronic tau decays - New inclusive analysis using lattice QCD data -, 06 Dec. 2016, 05 Dec. 2016, 08 Dec. 2016
- Hiroshi Ohki, The 14th International Workshop on Tau Lepton Physics (Tau2016), Lattice calculation of |Vus| from inclusive strangeness changing τ decay, 19 Sep. 2016, 18 Sep. 2016, 23 Sep. 2016
- Hiroshi Ohki, The 34th annual “International Symposium on Lattice Field Theory (Lattice 2016), |Vus| from inclusive strange τ decay data and lattice HVPs, 28 Jul. 2016, 24 Jul. 2016, 30 Jul. 2016
- Hiroshi Ohki, 2016年理研シンポジウム「スーパーコンピューターHOKUSAIとShoubu, 研究開発の最前線」, Precise Calculation of Nucleon Structure for Universe's Matter Dominance, 08 Jun. 2016, 08 Jun. 2016, 08 Jun. 2016
- Hiroshi Ohki, Lattice for Beyond the Standard Model Physics 2016, Many-flavor QCD dynamics on the lattice, 21 Apr. 2016, 21 Apr. 2016, 22 Apr. 2016
- Hiroshi Ohki, RBRC Workshop on Lattice Gauge Theories 2016, Inclusive τ decay analysis with lattice HVPs, 10 Mar. 2016, 09 Mar. 2016, 11 Mar. 2016
- 大木洋; 上村尚平, 日本物理学会秋季大会, 低次元表現による連続フレーバー対称性から非可換離散群への自発的破れ, 16 Sep. 2021, 14 Sep. 2021, 17 Sep. 2021, rm:research_project_id
- Hiroshi Ohki, The 38th International Symposium on Lattice Field Theory (Lattice2021), Hybrid stochastic method for the tensor renormalization group, 28 Jul. 2021, 26 Jul. 2021, 30 Jul. 2021, rm:research_project_id;rm:research_project_id

- 2018, 2021, 18H03710, Coinvestigator
- Grant-in-Aid for Scientific Research (A), 01 Apr. 2018, 31 Mar. 2022, 18H03710, Quark-hadron duality in B meson semileptonic decays, 橋本 省二; 大木 洋, Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), High Energy Accelerator Research Organization, 43810000, 33700000, 10110000, 本研究計画は、B中間子のインクルーシブ崩壊振幅の評価に格子QCDに非摂動計算を応用する理論的枠組みを構築することを目指している。インクルーシブ崩壊とは、終状態を特定せずすべての可能な終状態について足し上げたものを表す。この過程に対応する構造関数は、光学定理によってB中間子の前方散乱行列要素（２つの演算子を挟んだ行列要素）の虚数部に関係付けられる。この行列要素の解析性を利用して格子QCDで計算可能な量と関係をつけることが、この研究計画の基本的なアイデアである。 平成３０年度においては、格子QCD計算によって行列要素の計算を進め、複数の運動量移行についてデータを取得した。ただし、離散化誤差が大きくなり過ぎるのを防ぐため、ボトムクォークの質量は現実のものよりも軽く取って、手法の確立を優先することとした。 これと同時に、対応する摂動的計算の手法開発を進めた。これは、既存の摂動計算がどれだけの誤差をもつかを確認するためのもので、これまでの計算の信頼性を検証することを目的とするものである。, rm:published_papers;rm:misc;rm:presentations
- Grant-in-Aid for Young Scientists (B), 01 Apr. 2017, 31 Mar. 2021, 17K14309, 物質優勢宇宙の起源解明に向けた素粒子原子核の非摂動的計算, 大木 洋, Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B), Nara Women's University, 4160000, 3200000, 960000, 宇宙の起源の謎を解明するための重要な事象として初期宇宙の電弱相転移現象の解明が挙げられる。特にある種の素粒子標準模型を超えた新物理模型では未知の強い一次相転移が起こる可能性が示唆されており、そうした強い宇宙論的一次相転移が生じた場合、真空の相転移に伴う真空泡生成によって重力波が生成されると考えられる。そのような背景重力波を捉えようとする観測実験が現在計画中であり、標準模型を超えた未知の物理の探索とその重力波シグナルの理論的予測を行うことが重要である。本年度は、強結合ゲージ理論によって電弱相転移が動的に引き起こされる複合ヒッグス模型の一つであるウォーキングテクニカラー模型に着目し、その低エネルギー有効理論の構築、及びその宇宙論的相転移の性質を研究した。その結果、初期宇宙において強い一次相転移を引き起こし、将来の実験において観測可能な重力波シグナルを誘導する可能性があることが分かった。このような未知のゲージ理論を用いた研究は、元々進めてきた非摂動効果を含めた定量的な計算法である格子ゲージ理論における我々の先行研究の成果に基づくものであり、今後も様々な素粒子現象論への応用が期待される。また並行して強い相互作用の源である量子色力学(格子QCD)に応用する研究も同時に進めており、特に核子を用いた電磁双極子能率(EDM)はCP対称性の破れを示す重要な物理現象であり、その理論的解明が重要である。本年度は核子のEDMと密接に関連する重要な物理量である核子のテンソル電荷に着目し、そのストレンジクォークの寄与が本質的であるクォーク非連結ダイアグラムの効果も含めた数値計算を、厳密な格子上のカイラル対称性を保つオーバーラップフェルミオンを用いた格子QCDで行った。またQCDのθパラメータによる核子EDMの格子QCD計算も進めており、現実的なクォーク質量での高精度決定を行う研究を進めている。, rm:published_papers;rm:published_papers;rm:misc;rm:books_etc
- Grant-in-Aid for Young Scientists (B), 01 Apr. 2013, 31 Mar. 2016, 25800139, Lattice Numerical simulation of strong gauge dynamics for beyond the standard model, Hiroshi Ohki, Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B), 4030000, 3100000, 930000, Non-perturbative nature of many-flavor QCD through the numerical simulation of the lattice gauge theory within the framework of the (walking) technicolor model has been investigated. Many-flavor QCD is a good candidate for the walking technicolor, where the flavor singlet scalar can be regarded as a technidilaton, a pseudo Nambu-Goldstone boson of the approximate scale symmetry. In this work, we studied the flavor dependence of the low-energy behavior systematically in comparison with various number of flavor Nf=(0), 8, 12 based on a unique lattice setup. We discovered a signal of a flavor-singlet scalar meson lighter than the pseudo scalar in Nf =12 case. In Nf =8 case, we also observed a flavor-singlet scalar with mass comparable to or slightly smaller than that of the pseudo scalar in the fermion mass range of our simulations. This is a hint of the technidilaton as a composite Higgs to be identified with the Higgs boson which was discovered at LHC., kaken_url
- Grant-in-Aid for JSPS Fellows, 2009, 2010, 09J00897, 素粒子論におけるフレーバー構造の解明とその起源について, 大木 洋, Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows, 1400000, 1400000, 本研究の目的は、素粒子論におけるフレーバーの複雑な構造の起源を調べ、高エネルギー領域からの具体的な導出を目標とするものであった。初年度目では、クォーク・レプトンに存在する大きな世代間質量階層性の問題に対し、余剰次元内での各世代の場の局在から指数的に減少する湯川結合が得られるというモデルの研究を行った。特に現象論的に有望な背景磁場を持つ余剰次元モデルから、様々な離散的対称性が得られる事を見出した。これは高エネルギー理論と素粒子標準模型との関連性において、重要な示唆を与えるものであり、重要な研究成果であると言える。また本年度は、フレーバー構造と密接に関連する質量の起源に関する研究を行った。フレーバー構造を議論する上でヒッグス粒子の真空期待値は重要なパラメータであり、ヒッグス粒子の真空期待値、すなわち電弱対称性の破れを引き起こす機構として、強いゲージ相互作用を伴った動的な破れが、近年注目されている。そうした動的な破れは場の理論の非摂動的効果が重要であるため、格子ゲージ理論による数値計算が必要となる。そこで、本年度は格子理論におけるゲージ結合定数の有効な測定法を研究し、また具体的なQCDのモデルの数値計算に適用し、その手法の有効性を明らかにした。これにより、従来よりも精密な決定が可能となり、上記のモデルの計算に応用する事が可能である。現在はこれらの研究成果を踏まえ、幾つかの具体的なモデルにおけるゲージ結合定数の計算、フェルミオン双一次形式の異常次元、擬スカラー場の質量の測定等を行っており、現実的なフレーバー構造を持ちうるモデルの探索とその検証へと進展させていく予定である。
- 基盤研究(C), 01 Apr. 2021, 31 Mar. 2026, 21K03554, 格子非摂動ダイナミクスによる宇宙起源の探求, 大木 洋, 日本学術振興会, 科学研究費助成事業 基盤研究(C), 奈良女子大学, 4030000, 3100000, 930000, rm:published_papers;rm:presentations;rm:presentations